1. Field of the Invention
This invention relates to a displacement generating apparatus, and more particularly to a displacement generating apparatus in which bimorph-type piezoelectric elements are employed.
2. Description of the Prior Art
Conventionally, piezoelectric elements have been widely used as actuators in precise positioning applications where displacements of the order of microns and submicrons are desired. This is because such minute displacements can be relatively easily obtained by controlling voltages applied across the elements. However, when relatively large displacements are desired, such elements cannot be used without modifications. For example, in an application of a so-called STM (scanning tunneling microscope), a universal stage on which an object to be observed is placed is positioned in the following manner. First, a coarse positioning and then a fine positioning are cooperatively performed. However, the displacement of a piezoelectric element is too small to achieve the coarse positioning. Thus, other particular coarse positioning apparatus must be additionally provided. To solve this problem, an inchworm actuator has been used. The operational principle of the inchworm actuator is similar to that of the human waling operation. Specifically, the inchworm actuator operation is based on the combination of vertical and horizontal movements.
FIG. 10 shows a conventional displacement generating apparatus for use in an inchworm actuator application. In FIG. 10, v represents a vertical direction, and h represents a horizontal direction. The conventional apparatus has two pairs of bimorph-type piezoelectric elements 2a and 2b, and 3a and 3b, respectively adhered to an L-shaped elastic member 1. The pair of elements 2a and 2b serve to move in the vertical direction, and the pair of elements 3a, and 3b serve to move in the horizontal direction. One end of the member 1 is fixed to a support member 4, and the other end of the member 1 has a displacement force transmitting adapter 5. Further, a pair of electrodes 8a and 8b are formed on the outer sides of the elements 2a and 2b. Similarly, a pair of electrodes 9a and 9b are formed on the outer sides of the elements 3a and 3b. These elements 2a, 2b, 3a and 3b have been polarized in the directions indicated by arrows shown in FIG. 10. The electrodes 8a and 8b are respectively connected to a vertical-direction drive power source 7a through leads 6c and 6d. The electrodes 9a and 9b are respectively connected to a horizontal-direction drive power source 7b through leads 6e and 6f. The L-shaped elastic member 1, which also serves as a common electrode, is connected to the power sources 7a and 7b through leads 6a and 6b, respectively. When voltages Vv and Vh are supplied from the power sources 7a and 7b to the elements 2a, 2b, 3a and 3b, the member 1 is deformed on the whole into a shape indicated by a dotted line shown in FIG. 10. In other words, the apparatus generates displacements such that the adapter 5 simultaneously displacements such that the adapter 5 and a horizontal-direction displacement. These displacements are controlled by the voltages Vv and Vh. A plurality of the above-described displacement generating apparatus constitute a conventional inchworm actuator.
As described above, the conventional displacement generating apparatus is basically of a cantilever structure. Thus, the apparatus has low rigidity and a low resonance frequency, and can produce only a small force. Further, the displacement force transmitting adapter 5 inevitably moves in a rotational direction. Thus, the adapter 5 cannot be moved independently in the vertical and horizontal directions. Therefore, when this apparatus is employed in an inchworm actuator, certain disadvantages arise. Specifically, the inchworm actuator can carry only a lightweight object at a low speed. Further, the positioning of the object cannot be accurately performed.